A vehicle body has a structure in which a plurality of molding panels is bonded into a box shape by, for example, resistance spot-welding while edge portions of the molding panels overlap one another. A reinforcing member or a strengthening member (hereinafter, generally referred to as a “reinforcing member”) is bonded to the box-shaped structure by, for example, resistance spot-welding. As such vehicle body reinforcing members, there are a bumper reinforcement, a locker (side sill), a beltline, a cross member, and a side member.
Each of these reinforcing members is formed as, for example, a press-molded member that has a substantially hat-shaped or groove-shaped cross-section and includes a ceiling plate, two ridge lines connected to the ceiling plate, and two flanges connected to two ridge lines. An end portion opened in the extension direction of the ridge line of such a reinforcing member is bent inward or outward so as to form a flange in the end portion. When the flange overlaps the other member and the flange and the other member are bonded to each other by, for example, resistance spot-welding, a vehicle body reinforcing member is assembled. Depending on the plate thickness of the material, arc-welding may be used instead of spot-welding.
Here, in the specification, a flange obtained by bending the end portion of the reinforcing member toward an area in which an angle formed by two surfaces respectively connected to both ends of the ridge line is smaller than 180° will be referred to as an inward flange. Further, a flange obtained by bending the end portion of the reinforcing member toward an area in which an angle formed by two surfaces respectively connected to both ends of the ridge line is larger than 180° will be referred to as an outward flange.
When the inward flange is formed in the end portion of the reinforcing member, a ridge-portion flange located on the extension line of the ridge line is molded as a flange by shrinking, and hence wrinkles are generated in the ridge-portion flange. For that reason, when such an inward flange overlaps the other member and the inward flange and the other member are bonded to each other by spot-welding, a gap is generated between the inward flange and the other member due to the wrinkles, and hence there is a concern that an assembling problem may occur. Thus, when the reinforcing member having the inward flange formed at the end portion is used, there is a need to weld the reinforcing member to the other member by using the inward flange as a bonding edge while avoiding the generation of wrinkles by, for example, forming a notch in the ridge-portion flange.
However, when the notch is formed in the inward ridge-portion flange so that the flange is not continuous, the performance of the vehicle body reinforcing member involved with torsional rigidity or load transfer efficiency is essentially degraded. Thus, in order to ensure the performance demanded for the reinforcing member by bonding the reinforcing member to the other member through the inward flange, there is a need to mold the shrinking flange while suppressing the generation of wrinkles in the ridge-portion flange without any notch formed in the inward flange.
In addition, in the specification, the “notch formed in the flange” indicates a state where the notch is formed in the entire flange in the width direction so that the flange is not continuous. Further, the width of the flange is used as the meaning of the height of the flange. Thus, when the width of the flange is partially decreased so that a part of the flange is left, the notch is not formed in the flange.
So far, a technique of suppressing the generation of wrinkles during the shrinking flange molding process has been proposed. For example, Patent Literature 1 discloses a technique of forming an unevenness shape, absorbing a difference in length between a front end portion and a base portion in a shrinking flange portion, in a roof panel having a sunroof opening. Further, Patent Literature 2 discloses a technique of preventing the generation of wrinkles by providing a specific drawing bead in a shrinking flange portion during a rectangular tube drawing process. Furthermore, Patent Literature 3 discloses a technique of suppressing the generation of wrinkles by performing a molding process while applying a pressure to a shrinking flange portion using a cam structure.
Further, Patent Literature 4 discloses a plate member molding method in which a flange corresponding portion extending in a direction interesting a bending load direction is formed in a portion to be used as a bent portion and the flange corresponding portion is stretched into a flange so as to have a desired shape. Such a plate member molding method is used to suppress tearing caused by the wrinkles in the flange.
Patent Literature 5 discloses a method in which a plane metal member is bent, upright portions of both side portions are bent outward, and both inclined side portions are strongly pressed by a processing roller of a pressing surface of a side surface of a receiving die so as to be sequentially raised. Such a processing method is used to reduce the distortion or the wrinkles of the upright portion.